48 S. ZUCKERMAN 



suddenly appeared). To some extent it is a matter of taste 

 which view one accepts ; my own is for the simpler proposition 

 that the identities of apples — and equally of oocytes — cannot 

 be so simply switched. 



What answer should, then, be given to the question whether 

 oocytes continue to be formed in the adult ovary? If we set 

 aside for a moment some of the cytological evidence, the 

 experimental data undoubtedly support the view that as a 

 rule the mature mammalian ovary is incapable of adding to 

 the store of oocytes with which it is furnished by the time of 

 puberty. Most of this evidence has been derived from work 

 on rats, but the more fragmentary observations that have 

 been made on other species agree far more with this thesis 

 than they do with the contrary one. There appear to be 

 certain notable exceptions, and it may well be that oogenesis 

 ceases in some species earlier than in others, in which it may 

 continue for some time after puberty. But in general the ovary 

 appears to be a transient tissue which, so far as its main 

 function of oogenesis is concerned, has little or no powers of 

 regeneration once puberty has been reached. Compared with 

 the testis, the ovary is in this respect a structure which reaches 

 senescence early, and which cannot be rejuvenated by any 

 known hormonal treatment. 



Ovarian secretion 



This limitation does not extend, in any corresponding 

 measure, to the ovary's powers of hormonal secretion. These 

 normally manifest themselves first at the time of puberty, and 

 in woman they fade out at the menopause. In the interval 

 between these two temporal events, the ovary's capacity to 

 secrete hormone is under the control of the gonadotrophic 

 secretions of the pars distalis of the pituitary. Its capacity to 

 respond to this stimulation is often held to be independent of 

 the presence of germinal elements, but the evidence bearing 

 on this point is somewhat equivocal. Thus, in rats, an 

 ovarian graft that is apparently devoid of oocytes may some- 

 times secrete sufficient oestrogen to provoke continuous or 



